EPR of Mn2+pairs in MgO and CaO

Abstract

Nearest neighbour Mn²⁺ pairs in MgO and CaO have been studied using EPR. The isotropic exchange interaction measured in MgO cannot be written in the simple form Js_i.s_j and it is shown that although a small contribution due to intrinsic biquadratic exchange is possible, the anomalous effect arises mainly as a result of exchange striction. This exchange striction is found to be consistent with a variation of J with ionic separation r given approximately by J=J₀ exp(-19r/r₀), and this variation gives good agreement with exchange interactions deduced for MnO. Exchange striction effects also appear in the crystal field interactions and in the magnetic dipole-dipole interactions for both pair systems.